Xizi Gong¹, Guanpeng Chen¹, Ruolin Yang¹, Shenshen Zhang¹, Xiongfei Wang², Qian Wang¹, Fang Fang¹; ¹Peking University, ²Sanbo Brain Hospital, Capital Medical University

Integrating color and form into unified object representations is a fundamental challenge for human vision. However, the cortical stage at which this binding occurs remains debated. While classical theories posit that the V1 processes color and orientation via largely segregated neuronal populations, recent macaque studies suggest these features are jointly encoded at this early stage. Yet, the critical lack of single-neuron evidence in humans leaves the mechanisms of this integration unknown. Here, we report findings from a unique large dataset of over 600 neurons recorded from human V1. We demonstrate that a substantial subset (~20%) of neurons exhibits co-tuning to both color and orientation. Going beyond linear co-tuning, we identify significant non-linear interactions at the single-neuron level, indicating that chromatic context dynamically modulates orientation tuning. Furthermore, by characterizing the population geometry, we show that the interaction between hue and orientation accounts for a substantial fraction of the total signal variance, suggesting that feature conjunctions are explicitly represented rather than independently processed. These results provide the first single-neuron evidence in humans that color and orientation are jointly represented in V1.